My Piano Plays Like a Truck

So many vintage pianos have been restored with modern, heavy hammers,
but action parts designed for much lighter hammers. Those actions
typically have shallow key dip and are:

Exceedingly hard to control in soft dynamics, feeling as if they
are pushing the fingers out of the keyboard, and/or:

Repeat poorly and are inert and fatiguing in loud playing

Properly matched hammers and action parts, even when the hammers are
relatively heavy (as they are in many of the finest modern
grands) can be balanced so that the
action feels light and smooth, enabling excellent control down to the
softest pianissimo, while allowing effortlessly executing big, repeated
chords and difficult loud passagework.

Light Hammers

Some pianists and piano technicians recommend reproducing the
light weight of hammers from pre-WW II pianos because their sound is cleaner
and less aggressive, and their actions are very easy
to play. That is certainly true. One only needs to play a few passages
and glissandos on such a piano to realize how much easier it was to
play demanding Romantic literature a hundred years ago.

However, one also needs to be aware of the limitations of
that approach:

The relatively high leverage ratio of vintage actions
makes it more difficult to control dynamic nuances because it takes less
force (technically, "work") to reach fortissimo

The shallower key dip can be frustrating to a pianist who is
used to "digging into" the keys on modern pianos

Light hammers sound very clean, but also somewhat nasal and limited
in terms of expression in loud dynamics—there is a sense of tone
breaking up earlier on the dynamic scale, in forte rather than
fortissimo